Humidity, or water vapour in air, is often undesirable as it may interfere with the storage of moisture sensitive materials, such as foodstuffs, cosmetics, pharmaceuticals, household goods and clothes, or it may adversely effect the operation of moisture sensitive equipment. This problem may be particularly pronounced in those areas where humidity levels are particularly high, such as those countries having hot humid climates.
It is therefore often desirable to dehumidify air. Traditional methods for dehumidifying air include the use of mechanical refrigeration equipment and water absorbent materials, such as silica gel.
Typically, methods employing refrigeration equipment involve cooling air to a predetermined temperature below its dew point, so that water condenses from the air and the water may be drained away. Thereafter, the air may be reheated to a predetermined warmer temperature. Techniques including absorbent materials may include continuous operation systems so that water is absorbed by the absorbent in a first cycle and then water desorbed from the absorbent by the application of heat in a second cycle.
Suitably, these techniques suffer from various disadvantages as they typically require bulky and heavy equipment, such as compressors, fans and heaters, which are interconnected by a network of pipes so that water vapour is absorbed continuously from air. Typically, such systems are ill-suited for operation in a confined or limited space. Moreover, the cost associated with such systems may prohibit their use in a domestic environment.
In an attempt to overcome the disadvantages associated with using the aforementioned systems in a confined or limited space, alternative techniques have been developed that include exposing air to an absorbent material. In particular, portable smaller devices comprising a container housing an absorbent material have been employed for dehumidifying air in a limited or confined space, particularly in a domestic environment.
Although absorbents such as silica gel may be employed in these devices, typically silica gel only absorbs up to 30% its weight of water and it is necessary to employ an absorbent having a higher capacity for water vapour absorption to prolong the life and improve the efficiency of the device. Suitably, hygroscopic deliquescent agents, such as calcium chloride, which may absorb 4 to 5 times its weight of water, have been employed in such devices. Upon prolonged exposure to water vapour, typically in the order of days, the degree of saturation of the deliquescent agent increases and the deliquescent agent forms a liquid of gel, and is such that liquid seeps from it. Typically, the deliquescent agent is placed on a perforate shelf in the container so that the liquid drips into a region of the base of the container, thereby providing an indication that the container is functioning satisfactorily.
Although these devices have gone some way to solving the problems associated with absorbing water vapour in a confined space, particularly in a domestic environment, a major disadvantage with these devices, particularly those employing a deliquescent agent, is that they only provide the user with an indication that the device is functioning satisfactorily after it has been placed in a humid environment for prolonged periods of time. Typically, these devices do not provide the user with an early indication that the device is functioning satisfactorily shortly after being placed in a humid environment, because it typically takes a number of days before the deliquescent agent reaches a level of saturation to form a liquid or gel.